This invention relates in general to locking apparatus, and in particular to apparatus for locking sliding panel doors such as patio doors or the like.
So-called "patio doors" generally include a pair of panel members, usually made of glass, mounted in coplanar relation within a frame. One of the panels is usually supported for sliding movement relative to the other panel, within a track typically contained in or formed by the frame, so that the door panel can be slidably opened or closed relative to the fixed panel. Patio doors have found widespread acceptance in houses and apartments, due to the ease of opening a relatively large area and the amount of daylight illumination provided by such doors.
The popularity of the conventional patio door has caused corresponding problems in home security, because these doors in conventional construction are relatively susceptible to unauthorized opening by intruders or the like. Although most sliding patio doors come equipped with some type of locking mechanism, the typical standard-equipment patio door lock may be relatively flimsy and easily jimmied or broken by an experienced burglar. Some such locks can be thwarted simply by inserting a thin object such as a knife blade between the door frame and the forward edge of the door, so as to withdraw a spring-loaded latch. Patio door locks having a deadbolt type of construction, which cannot be jimmied in the foregoing manner, can nevertheless be overcome simply by inserting a pry bar between the frame and the adjacent door edge, and then forcing the two elements apart until the bolt is withdrawn from the frame.
Various devices have been proposed in the art for increasing the locking security of a patio door, so that an intruder or other unauthorized person cannot force the door unless he resorts to smashing the entire glass panel. One such prior-art locking device, known as the "Charley bar", is shown in U.S. Pat. No. 3,328,920, and consists of a locking bar that may be inserted between a pair of brackets, one bracket being attached to the movable door panel and the other bracket being attached to a stationary member such as the frame or the like. While locking devices such as the Charley bar are relatively effective for securing a patio door in the fully-closed position, many people also want to securely lock their patio door slightly ajar. For example, a person having household pets may wish to secure the patio door ajar so as to leave an opening too small for a human to pass, but sufficiently wide to allow a cat or small dog to enter or leave. Other persons may simply desire to leave a patio door ajar for ventilation at night time or while they are away from home, without leaving the patio door unlocked or subject to forceable entry.
While devices have been proposed in the art that permit adjustable closure locking of patio doors, such devices are believed to have been generally impracticable due to expense, complexity, or difficulty of installing without mutilating the structure of the door.